Hydrogenation of high boiling hydrocarbons

ABSTRACT

.[.In a hydrogenation operation employing an ebullated catalytic bed, recycle is recovered from the hydrogenated product with at least 25%, by volume, of the recycle boiling above 950° F. The recycle is cooled to a temperature of from 350° to 600° F. to separate coke precursors, prior to recycle to the hydrogenation. Higher conversion levels can be achieved by effecting recycle in such manner..]..Iadd.Disclosed is a hydrogenation process using at least one fluidized catalytic stage and a recycle material of heavy hydrogenated effluent. The heavy effluent material is cooled to a temperature within 350°-600° F. to separate toluene and heptane insoluble coke precursors prior to recycle. This separation may be enhanced by the use of centrifugation, filtration or a bed of particulate material (e.g. calcined coke). .Iaddend.

This application is a .Iadd.reissue of U.S. Pat. No. 4,411,768, Ser. No.370,416 which is a .Iaddend.continuation-in-part of U.S. applicationSer. No. 272,720, filed on June 11, 1981, now abandoned, with theaforementioned application being a continuation of U.S. application Ser.No. 106,274, filed on Dec. 21, 1979, now abandoned.

This invention relates to hydrogenation, and more particularly to thehydrogenation of high boiling hydrocarbon materials to provide valuablelower boiling materials.

High boiling hydrocarbon materials, derived from either petroleum orcoal sources, typically petroleum residuum or solvent refined coal, arehydrogenated in an ebullated (expanded) catalyst bed in order to producemore valuable lower boiling materials. In general, the conversion levelsfor such an operation are limited by a tendency to form heavycarbonaceous deposits which result in agglomeration of the catalyst. Thelimit is at a different conversion level for each feedstock.

As a result, there is a need for an improvement in such hydrocarbonprocesses in order to permit operation at higher conversion levels.

In accordance with the present invention, there is provided animprovement in a process for upgrading high boiling hydrocarbonmaterials to valuable lower boiling materials in an ebullated catalyticbed, wherein recycle is recovered from the upgraded product and at least25%, by volume, of the recycle is comprised of the 950° F.⁺ componentsof the product. The liquid recycle is cooled to a temperature of atleast 350° F. (most generally at least 400° F.) and no greater than 700°F. (most generally no greater than 600° F.) to separate coke precursorsfrom the liquid recycle, prior to introduction thereof into theebullated catalytic bed of the hydrogenation operation. Applicant hasfound that by providing recycle in this manner the operability range ofthe hydrogenation reaction can be extended to operate at higher levelsof conversion.

As hereinabove noted, at least 25%, by volume, of the recycle boilsabove 950° F. In most cases, the 5-volume percent distillationtemperature of the recycle is at least 450° F., preferably at least 550°F., and most preferably at least 600° F. The recycle may be convenientlyprovided by recovering from the product a 550° F.⁺ fraction. It is to beunderstood, however, that the recycle could be a higher boilingfraction; for example a 600° F.⁺ fraction (the 5-volume percentdistillation temperature is at least 600° F. and at least 25-volumepercent boils above 950° F.), or a 1000° F.° fraction (the 5-volumepercent distillation temperature is at least 1000° F.). The recycle isprovided as a high boiling recycle in order to minimize the ratio of the300° F.-550° F. distillate to the 1000° F.⁺ residue in the liquid phasein the last hydrogenation zone.

In accordance with the present invention, the liquid recycle is treatedto remove coke precursors by cooling of the liquid recycle to apreferred temperature of from 350° to 600° F., with such coolingseparating coke precursors from the liquid recycle. Coke precursors,which are characterized as being toluene insolubles and heptaneinsolubles, precipitate from the liquid recycle at such temperatures,and by maintaining the liquid recycle at such temperatures for asufficient length of time, it is possible to effectively separate andremove such coke precursors from the liquid recycle.

The removal of such coke precursors may be enhanced by a filtration orcentrifugation operation; however, it is possible to separate such cokeprecursors from the liquid recycle without such operation.

It is also possible to enhance the removal of such coke precursors fromthe liquid recycle at the hereinabove specified temperatures by adding alow boiling liquid to the liquid recycle to reduce the solubility of thecoke precursors.

After separating such coke precursors from the liquid recycle, theliquid recycle may be introduced into the ebullated catalytic bed of thehydrogenation reactor, along with the feed thereto, and by separatingsuch coke precursors from the liquid recycle, it is possible to achievehigher conversions, without plugging of the catalyst bed.

In accordance with an embodiment of the invention, the liquid recyclemay be cooled to temperatures as hereinabove described, and passedthrough a bed of particulate material which provides a surface on whichthe coke precursors may be deposited to thereby facilitate theseparation of such coke precursors from the liquid recycle. It is to beunderstood, however, other surfaces may be used for depositing such cokeprecursors; accordingly, the scope of the embodiment is not limited tothe use of particulate material.

The present invention has particular applicability to a hydrogenationprocess which is to operate at high conversions; i.e., conversions ofgreater than 60%, and in particular conversions greater than 70%;however, it is to be understood that the present invention would also beapplicable to hydrogenation processes employing an ebullated catalystbed, which are operated at lower conversions.

The upgrading of the high boiling hydrocarbon materials by hydrogenationin an expanded bed catalytic hydrogenation zone is conducted attemperatures and pressures, and with a catalyst, as generally known inthe art; however, by proceeding in accordance with the presentinvention, it is possible to operate at conversion levels higher thanpreviously employed in the art, without adversely affecting the overalloperation. In general, the hydrogenation is conducted at a temperaturein the order of from about 650° to about 900° F., preferably from about750° to about 850° F., and at an operating pressure of from about 500psig to about 4000 psig, with the hydrogen partial pressure generallybeing in the order of from about 500 to 3000 psia.

The catalyst which is employed may be any one of a wide variety ofcatalysts for hydrogenation of heavy materials, and as representativeexamples of such catalysts, there may be mentioned: cobalt-molybdate,nickel-molybdate, cobalt-nickel-molybdate, tungsten-nickel sulfide,tungsten-sulfide, etc. with such catalyst generally being supported on asuitable support such as alumina or silica-alumina. Such catalyst ismaintained in the hydrogenation reactor as an expanded or ebullated bed,as known in the art. In view of the fact that hydrogenation in anebullated bed is known in the art, no further details in this respectare deemed necessary for a complete understanding of the presentinvention.

The recycle provided in accordance with the invention is employed in anamount whereby the ratio of recycle to total fresh feed to thehydrogenation is from about 0.2:1 to about 10:1, preferably from about0.4:1 to about 1.0:1. It is to be understood that each of thehydrogenation zones may or may not include an internal recycle dependingon the total flow to the zone. The amount of internal recycle, if any,is adjusted in accordance with the amount of external recycle providedin accordance with the present invention.

The feed to the process, as known in the art, is one which has highboiling components, which are to be converted to more valuable lowboiling components. In general, such a hydrocarbon feed has at least25%, by volume, of material boiling above 950° F. Such feed may bederived from either petroleum and/or coal sources, with the feedgenerally being a petroleum residuum, such as atmospheric tower bottoms,vacuum tower bottoms, heavy crudes or tars containing small amounts ofmaterial boiling below 650° F., or a solvent refined coal, and the like.The selection of a suitable feedstock is deemed to be within the scopeof those skilled in the art, and as a result, no further details in thisrespect are deemed necessary for a complete understanding of the presentinvention.

The expanded bed catalytic hydrogenation may be accomplished in one, twoor more zones, and if there is more than one zone, the recycle, aftertreatment to remove coke precursors, as hereinabove described, isprovided to at least the last of the two hydrogenation zones. Therecycle may be provided to the at least last of the two hydrogenationzones. The recycle may be provided to the at least last zone by directlyintroducing the recycle into the last zone or all or a portion thereofmay be introduced into a preceding zone, whereby all or a portion of therecycle to the last zone is provided with the effluent from thepreceding zone or zones in the series.

The present invention will be further described with respect to apreferred embodiment thereof illustrated in the accompanying drawing,wherein:

The drawing is a simplified schematic flow diagram of an embodiment ofthe present invention.

It is to be understood, however, that the scope of the invention is notlimited to such preferred embodiment. Thus, for example, although theembodiment is described with respect to the use of two hydrogenationzones, the invention is equally applicable to the use of a singlehydrogenation zone, or to the use of more than two hydrogenation zones.

Referring now to the drawing, a hydrocarbon feed to be upgraded, in line10, is combined with recycle in line 11, if employed as hereinafterdescribed, and the combined stream in line 12 passed through a heaterwherein the combined stream is heated to an appropriate hydrogenationinlet temperature, e.g., a temperature in the order of from 600° F. to800° F. The heated hydrocarbon feed, in line 14, is combined with agaseous hydrogen containing stream, in line 15, and the combined streamin line 16 introduced into the bottom of the first of two ebullated bedhydrogenation reactors 17 and 18.

The reactors 17 and 18 are of a type known in the art, and may includemeans 21, in the form of an internal tube, provided with a pump at thebottom thereof, (not shown), for providing internal recycle within thereactor sufficient to maintain the flow for providing an ebullated orexpanded catalyst in reactors 17 and 18. If the flow of fresh feed andrecycle is sufficient to maintain an expanded catalyst bed, then theinternal recycle tube and pump can be eliminated. The reactor 17 isoperated at temperatures and pressures as known in the art, and ashereinabove described. Thus, the feed is passed upwardly through reactor17 in contact with the hydrogenation catalyst therein, and the effluentis withdrawn from reactor 17 through line 22 for introduction into thesecond hydrogenation reactor 18.

The effluent in line 22 may be combined with recycle, as hereinafterdescribed in more detail, from line 23, in which case the recyclefunctions to cool the reaction effluent prior to the hydrogen quench.Alternatively, as hereinafter described, the recycle may be providedthrough line 24, subsequent to hydrogen quenching. The effluent, whichmay or may not contain recycle, is then quenched with hydrogencontaining gas in line 25, and the combined stream in line 26 is thenintroduced into the bottom of the second ebullated bed hydrogenationreactor 18.

The hydrogenation reactor 18 is operated at conditions as hereinabovedescribed to effect hydrogenation of the feed and upgrading thereof tolower boiling components. As particularly shown, reactor 18 is providedwith internal recycle; however as hereinabove described, the internalrecycle could be eliminated if the total flow is sufficient to maintainan expanded catalyst bed.

A reaction effluent withdrawn from reactor 18 through line 28 isintroduced into a gas separation zone, schematically generally indicatedas 29 in order to recover a hydrogen recycle gas from the effluent. Thegas separation zone may include one or more gas-liquid separators, andcoolers, as appropriate, in order to provide for separation and recoveryof the hydrogen recycle gas. Hydrogen recycle gas is recovered throughline 31 and after purging, as appropriate, and compression (not shown),and addition of make-up hydrogen through line 32, a portion of thehydrogen is provided to reactor 18 through line 25, and after heating inheater 33 to reactor 17 through line 15.

Liquid product from the gas separation zone 29, in line 35 is introducedinto a product separation and recovery zone, schematically generallyindicated as 36.

The separation and recovery zone 36 may include one or morefractionating towers, and/or separators, designed and operated torecover various products, and recycle streams, from the hydrogenationeffluent. In particular, in accordance with the present invention, thereis recovered a liquid recycle stream in line 37, having thecharacteristics hereinabove described; i.e., a 5-volume percentdistillation temperature of at least 450° F. with at least 25 volumepercent thereof boiling above 950° F. The recycle is preferably a 550°F.⁺ or 1000° F.⁺ fraction recovered from the product.

The recycle in line 37 is introduced into zone 38, wherein the recycleis cooled to a temperature of from 350° F. to 600° F. to separate cokeprecursors from the liquid recycle. In accordance with a preferredembodiment, the cooled recycle is passed through a bed of particulatematerial, such as, for example, calcined coke, to deposit theprecipitated coke precursors on such solids.

The recycle from zone 38 is then employed in lines 11 and/or 23 and/or24 in order to provide recycle to the last reactor 18. Thus, all or aportion of the recycle to reactor 18 may be provided directly to reactor18 or indirectly through reactor 17.

It is to be understood that the hereinabove described embodiment may bemodified within the spirit and scope of the present invention. Thus, forexample, separation of the coke precursors may be enhanced by providingfiltration and/or centrifugation, and/or a low boiling solvent in zone38.

Thus, in accordance with the present invention external recycle isprovided to the last reactor of the series and such recycle ispretreated to remove coke precursors and has boiling characteristics tominimize in the liquid phase of the last reactor the ratio of the300°-500° F. distillate to the 10,000° F.⁺ residue.

The present invention will be further described with respect to thefollowing example; however, the scope of the invention is not to belimited thereby:

EXAMPLE

The following is illustrative of conditions for hydrogenation of areduced crude, employing three expanded bed reactors in series. Thecatalyst is nickel molybdate supported on alumina.

Operating Conditions of Reactors:

Temperature, °F.--811

Pressure, psig--2250

Liquid Feed, lb./hr.--3.98

Hydrogen Rate, SCFH--59

Conversion of 975° F.⁺, Vol %--71.6

The recycle is a 550° F.⁺ fraction recovered from the hydrogenationproduct, which is contacted with calcined coke (6-20 mesh, bulk density43 lb/ft3) at a temperature of 550° F. The recycle is then heated to650° F. and introduced into the second and third reactors, with theratio of combined recycle to total fresh feed ranging from 2:1 to 10:1.

The present invention is particularly advantageous in that it ispossible to extend the range of operable conversion rates for a givenfeedstock. Thus, by operating in accordance with the invention, a higherrate of conversion may be employed without the difficulties heretoforeencountered in the art. Thus, in accordance with the present invention,hydrogenation of heavy hydrocarbon feedstock is effected at higherconversion rates, without an increase in pressure drop, or difficulty incontrolling reaction temperatures.

Numerous modifications and variations of the present invention arepossible in light of the above teachings and, therefore, within thescope of the appended claims, the invention may be practised otherwisethan as particularly described.

We claim:
 1. In a process for upgrading high boiling hydrocarbonmaterials to valuable lower boiling materials .[.is.]. .Iadd.in.Iaddend.a hydrogenation operation including at least one expanded bedcatalytic hydrogenation zone to produce an upgraded hydrogenatedproduct, the improvement comprising:recovering from the upgradedhydrogenation product a recycle liquid having a 5-volume percentdistillation temperature of at least 450° F. with at least 25 -volumepercent thereof boiling above 950°F.; cooling the liquid recycle to atemperature of at least 350° F. and no greater than 700° F. to.[.separate.]. .Iadd.precipitate coke precursors;.Iaddend..Iadd.removing essentially only .Iaddend.coke precursors fromthe .Iadd.cooled .Iaddend.liquid recycle; and subsequent to.[.separation.]. .Iadd.removal .Iaddend.of said coke precursorsproviding the liquid recycle to an expanded bed catalytic hydrogenationzone.
 2. The process of claim 1 wherein the cooled liquid recycle ispassed through a bed of particulate solids to deposit separated cokeprecursors on the solids.
 3. The process of claim 2 wherein the recycleliquid is a 600° F.⁺ fraction.
 4. The process of claim 1 wherein therecycle liquid is a 1000° F.⁺ fraction.
 5. The process of claim 1wherein the recycle is cooled to a temperature of at least 400° F. 6.The process of claim 1 wherein the recycle is cooled to a temperature ofno greater than 600° F. .Iadd.7. The process of claim 1 wherein thecooled liquid recycle is centrifuged to enhance separation and removalof coke precursors. .Iaddend. .Iadd.8. The process of claim 7 whereinthe recycle liquid is a 600° F.⁺ fraction. .Iaddend. .Iadd.9. Theprocess of claim 7 wherein the recycle is a 1000° F.⁺ fraction..Iaddend.
 10. The process of claim 7 wherein the recycle is cooled to atemperature of no greater than 600° F.